Received: 27 August 2019 | Revised: 4 February 2020 | Accepted: 20 February 2020 DOI: 10.1111/ahe.12549 SPECIAL ISSUE Cardiogenesis with a focus on vasculogenesis and angiogenesis Katrin Borasch1 | Kenneth Richardson2 | Johanna Plendl1 1Department of Veterinary Medicine, Institute of Veterinary Anatomy, Freie Abstract University Berlin, Berlin, Germany The initial intraembryonic vasculogenesis occurs in the cardiogenic mesoderm. Here, 2 College of Veterinary Medicine, School a cell population of proendocardial cells detaches from the mesoderm that subse- of Veterinary and Life Sciences, Murdoch University, Murdoch, WA, Australia quently generates the single endocardial tube by forming vascular plexuses. In the course of embryogenesis, the endocardium retains vasculogenic, angiogenic and Correspondence Johanna Plendl, Department of Veterinary haematopoietic potential. The coronary blood vessels that sustain the rapidly ex- Medicine, Institute of Veterinary Anatomy, panding myocardium develop in the course of the formation of the cardiac loop by Freie University Berlin, Berlin, Germany. Email: [email protected] vasculogenesis and angiogenesis from progenitor cells of the proepicardial serosa at the venous pole of the heart as well as from the endocardium and endothelial cells of Funding information Freie Universität Berlin the sinus venosus. Prospective coronary endothelial cells and progenitor cells of the coronary blood vessel walls (smooth muscle cells, perivascular cells) originate from different cell populations that are in close spatial as well as regulatory connection with each other. Vasculo- and angiogenesis of the coronary blood vessels are for a large part regulated by the epicardium and epicardium-derived cells. Vasculogenic and angiogenic signalling pathways include the vascular endothelial growth factors, the angiopoietins and the fibroblast growth factors and their receptors. KEYWORDS angiogenesis, cardiogenesis, development, heart, vasculogenesis 1 | INTRODUCTION 1993). In addition, cells of the cephalic mesoderm, neural crest and prechordal endoderm are also involved in the formation of the heart The complex heart of birds and mammals developed from the prim- (Chan et al., 2016; Hatzistergos et al., 2015; Kirby, Gale, & Stewart, itive, linear “pumping organ” of primordial vertebrate ancestors, 1983; Kirby et al., 2003; Noden, Poelmann, & Groot, 1995). such as the lancelet in the order Amphioxiformes (Romer & Parsons, During the development of the heart, vasculogenesis, which is 1986). It is the first functioning organ in a vertebrate embryo. Its the in situ development of a vascular plexus from endothelial pro- three layers, endocardium, myocardium and epicardium, mainly de- genitor cells, and angiogenesis, referring to the sprouting of blood velop shortly after gastrulation from an area of the mesoderm lo- vessels from already existing ones, both play important roles. The cated bilaterally to Hensen's node that is referred to as cardiogenic establishment of the endocardium, the internal lining of the heart, mesoderm (Garcia-Martinez & Schoenwolf, 1993; Linask & Lash, marks the initial commencement of intraembryonic vasculogenesis Parts of this review have been published in the doctoral thesis of Katrin Borasch “Neue Erkenntnisse der Embryologie zur Entwicklung des Herzens. Eine Literaturstudie” (Novel insights into cardiogenesis—a literature-based study); Dissertation thesis in German, Institute of Veterinary Anatomy, Department of Veterinary Medicine, Freie Universität Berlin; German language, 272 pages, 71 figures. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2020 The Authors. Anatomia, Histologia, Embryologia published by Wiley-VCH GmbH Anat Histol Embryol. 2020;49:643–655. wileyonlinelibrary.com/journal/ahe | 643 644 | BORASCH ET AL. (Drake & Fleming, 2000; Harris & Black, 2010; Patan, 2000). TABLE 1 Abbreviations and explanations Apart from a few key transcription and growth factors, little is Abbreviation Full name/explanation known about the regulatory networks orchestrating endocardial Ang Angiopoietin formation. BMP Bone morphogenetic protein(s) The outermost layer of the heart, the epicardial sheath, devel- ops during the formation of the cardiac loop, starting from a zone CD Cluster of differentiation of proliferation that is located at the venous pole of the heart. The COUPTFII Chicken ovalbumin upstream promoter transcription factor II epicardium and the subpopulation of epicardium-derived cells that originate from it ultimately migrate into the myocardium, where Cxcl12 C-X-C motif chemokine 12, synonym stromal cell- derived factor 1 they function as essential signal transmitters for vasculogenetic and Cxcr C-X-C chemokine receptor angiogenetic processes that occur in the subepicardium and myo- E Embryonic day of development cardium and also form the coronary blood vessels. The diverse and complex regulatory mechanisms of coronary vasculogenesis and eNOS3 Endothelial nitric oxide synthase 3 angiogenesis as well as the differentiation into venous and arterial Eomes Eomesodermin endothelia have been studied relatively extensively (Chen, Poduri, Eph Erythropoietin-producing hepatocyte receptor et al., 2014; Chen, Sharma, et al., 2014; Luttun & Carmeliet, 2003). Ephrin Ligand of Eph receptors However, the complicated transcriptional interaction of the differ- ETV2 Ets transcription factor variant 2 ent cell types involved as well as the complexity of the morphoge- FGF Fibroblast growth factor netical events does not allow simple clarification. FGFR Fibroblast growth factor receptor Flk1 Fetal liver kinase 1, synonym VEGFR2 Fog Friends of GATA 1.1 | Origin and segregation of cardiogenic GATA4 Gene encoding a member of the GATA family of progenitor cells zinc-finger transcription factors HH Hamburger Hamilton stage The cardiogenic subpopulation of mesodermal progenitor cells is lo- HIF Hypoxia-inducible factor cated in the E6.5 (embryonic day of development; for abbreviations, Isl, Islet Insulin gene enhancer-binding protein see Table 1) of the murine embryo (equals Hamburger Hamilton stage MesP Mesoderm posterior (HH) 3 in the avian embryo) in the anterior third of the primitive N Neural streak. Here, the cells are arranged anteroposteriorly in an order that corresponds to that identified in the subsequent heart tube [from an- Nkx2.5 NK2 homeobox 5, a protein coding gene terior to posterior: cells of the future ventricular outflow tract (previ- NFATc Nuclear factor of activated T cells ously designated bulbus cordis), the ventricles, the arteries and the PECAM Platelet endothelial cell adhesion molecule sinus venosus]. However, at this point in time, the cells have not set- RALDH Retinaldehyde dehydrogenase tled into their final location (Camp, Dietrich, & Munsterberg, 2012; Shh Sonic hedgehog Garcia-Martinez & Schoenwolf, 1993; Redkar, Montgomery, & Litvin, SMC Smooth muscle cells 2001). Even so, it is already possible to classify cells into those of the Tal1 T-cell acute leukaemia protein first (posterior cell location) and second (anterior cells) heart fields Tbx18 T-box transcription factor gene as well as to identify future myocardial, endocardial and epicardial Tie2 TEK receptor tyrosine kinase cells of the heart as well as smooth muscle cells of the cardiac blood VE Vascular endothelial vessels. A portion, <5% of the progenitor cells, predominately those VEGF Vascular endothelial growth factor of the second heart field, retain bipotent qualities (Devine, Wythe, VEGFR Vascular endothelial growth factor receptor George, Koshiba-Takeuchi, & Bruneau, 2014; Lescroart et al., 2014; Milgrom-Hoffman et al., 2011; Wei & Mikawa, 2000; see Figure 1). Wnt Wingless-related integration site Transcription factor eomesodermin (Eomes), which is induced WT Wilms tumour transcription factor by canonical Wnt (Wingless-related integration site) signalling, ac- tivates from E6.5 transcription factor MesP1 (mesoderm posterior 1) in the multipotent cardiogenic progenitor cells of the primitive 2014; Milgrom-Hoffman et al., 2011; Saga, Kitajima, & Miyagawa- streak (Costello et al., 2011; Van den Ameele et al., 2012). MesP1 Tomita, 2000; Saga et al., 1999). As a fundamental prerequisite for is regarded as the earliest marker (however not exclusively so) of the specification of these cells, it downregulates nodal expression the cardiovascular mesoderm and comprises progenitor cells of the and is involved in controlling several essential “key genes” of cardio- myocardium, endocardium and epicardium as well as the vascular genesis, such as Nkx2.5 and GATA4 (Bondue et al., 2008; Costello smooth muscle cells of the heart (Chan et al., 2013; Lescroart et al., et al., 2011; Lindsley et al., 2008). MesP1 expression irreversibly BORASCH ET AL. | 645 FIGURE 1 Illustration, where the outer circle indicates the blastodisc and the elongate rectangle is the primitive streak. Segregation of cardiogenic progenitor cells in the primitive streak; highlighted in red: progenitor cells of the first heart field (FHF), early MesP1 (mesoderm posterior 1) expression; highlighted in yellow: progenitor cells of the second heart field (SHF), late MesP1 expression; CMs, cardiomyocytes; ECs, endocardial cells; EPDCs, epicardium-derived cells; SMCs, smooth muscle cells. Modified from Lescroart et al. (2014) indicates the restriction of the development potential of cardiovas- Early